Beans and seeds: II
One is the teardrop-shaped pod produced by a grass named "Job's Tears" (botanically, Coix lacryma-jobi). This is usually referred to as a "seed," but it's actually a very hard, woody pod that forms around the tiny flowers of the grass. The seeds inside are high in protein, mild tasting and quite nutritious, and Job's Tears was historically grown in India and the Far East as a cereal grain (sometimes called aday). It's actually rather closely related to sweet corn (Zea mays).
The pods are naturally smooth and shiny, whitish gray, yellow, purple or brown, and they seem to take dyes fairly well. Conveniently for those who want to use them as beads, they already have a natural hole through the center. The teardrop shape is probably the reason for the name, and a lot of people appreciate the "tears" symbolism.
As with the other seeds I've mentioned, it's very difficult to know just when or where such seeds were first used to make rosaries. It's entirely likely that they were used first for jewelry and adopted for use as prayer beads just as many other jewelry materials have been.
Quite a different notable -- or perhaps I should say notorious! -- seed used in rosaries is the rosary pea or rosary bean (Abrus precatorius). The seeds are small, roundish, very hard, and brilliantly red with a black spot.
The reason this plant is so notorious is that the seeds contain a compound called abrin, one of the most toxic poisons in nature. The pea or bean family (Fabaceae), to which the rosary pea belongs, actually contains quite a few toxic plants with compounds of this general type, but this one is unusually potent.
Fortunately for all concerned, the poison is only released if the very hard seeds are chewed and swallowed, but a single seed could easily kill an adult human. The poison is also of a singlularly nasty type: rather like the poison of "death angel" mushrooms, it can bring active cell metabolism to a complete stop, causing the collapse of major body systems. There is not much that can be done to counteract this.
The rosary pea is native to India, and the Wayne's Word botanical website notes that, "Because of their remarkably uniform weight of 1/10th of a gram, seeds of Abrus precatorius were used by goldsmiths of East Asia as standard weights for weighing gold and silver. In fact, the famous Koh-i-noor diamond of India, now one of the British crown jewels, was reportedly weighed using seeds of Abrus precatorius."
The attractive red color means that rosary peas sometimes turn up as part of the seed necklaces commonly sold to tourists in tropical climates, and a warning about rosary peas used to be part of the U.S. Department of Agriculture's standard information for returning tourists -- I don't know if it still is.
Personally, I wouldn't recommend using them. Hopefully we are all too sensible to chew on our rosaries, but there are so many other possible materials with far less risk attached.